Six-port Receiver Research Articles

Novel calibration algorithm of six-port receivers based on radial basis function network

ABSTRACT In this paper, the radial basis function neural network based on the orthogonal least squares (OLS-RBFNN) method is proposed for the first time for the calibration of the six-port receiver, which realises six-port accurate reception in the true sense. This algorithm overcomes the problems of an ageing circuit, narrow working frequency band and nonlinearity of the six-port receiver hardware. The RBFNN is a three-layer forward network, including an input layer, a hidden layer and an output layer. The transformation function of the hidden layer is the radial basis function. A six-port receiver test platform with an operating frequency band of 2.0–8.0 GHz is built to verify the performance of the six-port receiver based on OLS-RBFNN. The test signal is a 16-QAM signal with different bandwidths and different frequency bands. The test indicator uses error vector magnitude (EVM)， which represents the error between the received signal and the ideal signal sent. At last, the EVM of all tested data is less than 1.07%, and the best EVM is 0.57%. Therefore, the calibration accuracy of the OLS-RBFNN proposed in this paper is very high.

An SISL-Based 24-GHz FMCW Radar With Self-Packaged Six-Port Butler Matrix Receiver

A 24-GHz frequency modulated continuous wave (FMCW) radar system with self-packaged six-port Butler matrix receiver using substrate integrated suspended line (SISL) platform is proposed in this article. Since all active and passive components are integrated on the SISL platform using the standard printed circuit board (PCB) process, the proposed system is highly integrated with low cost. The system is composed of a transmitting (TX) antenna, a Butler matrix with a receiving (RX) antenna array, a single pole four throw (SP4T) switch, a low noise amplifier (LNA), and a six-port receiver. The Butler matrix and SP4T switch are implemented for beam scanning, which has the advantages of low loss and compact size. The SISL-based six-port receiver is designed for quadrature downconversion. The supporting digital signal processing algorithms are also proposed for the calculation and display of multiple targets information. The radar system has shown excellent performance in the measurement of indoor environment, including range, velocity, and direction of arrival (DOA). The proposed radar provides a new solution for a transceiver system.

Design and Evaluation of a Low-Cost SAW Resonator Read-Out System at 2.4 GHz

The functionality of using surface acoustic wave (SAW) resonators in wireless sensing applications has been demonstrated in many publications. When used, their resonance frequency has to be determined with a precision of up to 10 ppm with measurement periods in the microsecond range. For this purpose, the so-called instantaneous frequency measurement (IFM) can be used, which uses a six-port receiver to measure a frequency-dependent phase delay. This work presents a system that incorporates an alternative low-cost circuitry that multiplexes the four six-port outputs on only one detection circuitry with the help of an RF switch. This reduces the system cost and eliminates the measurement errors otherwise caused by differing gain and group delay values in the baseband filters. Based on this idea, a complete SAW readout system is presented and experimentally evaluated, which also can be used as a sensor node as it incorporates a Bluetooth interface. The shown measurement results demonstrate that the system can achieve a precision of 7.9 ppm concerning frequency measurement at an update rate of 41.7 Hz, demonstrating the feasibility of the alternative detection circuit.

Accuracy-Enhanced Angle-of-Arrival Finding System Using Switched Six-Port Network

In this letter, a switched six-port (SP) receiver is proposed for an accurate angle-of-arrival (AoA) finding system. The proposed switched six-port network consists of four antennas, two hybrid couplers, two dual-pole-dual-throw switches, and four power detectors. The proposed switched six-port receiver periodically selects two different antennas from four antennas, providing four different antenna spacings for a more accurate AoA detection. As a result, a smaller and more accurate AoA finding system has been achieved than a conventional dual six-port receiver that uses two different antenna spacings from four antennas. For validation, the proposed method was simulated, implemented, and measured. In the measurement, the averaged root-mean-square error of the estimated angle over the range of $-\text{90}^\circ$ to $\text{90}^\circ$ was $\text{3.16}^\circ$ with 20 sample numbers and a signal-to-noise ratio (SNR) of 15 dB.

Dynamic range improvement of six-port receiver through analysis of output DC offset

In this paper, we improved the error vector magnitude (EVM) performance of six-port receiver using a low noise amplifier (LNA) bias control algorithm based on analyzing the correlation between normalized output DC offset voltage and EVM relative to input radio frequency (RF) power variation. In contrast to the other works published in the literature, we consider test setup through which the software impairments of six-port receiver blocks are considered. Therefore, in this work to substantiate the EVM improvement, a designed 26–30 GHz CMOS six-port receiver is used which consists of LNA, coupled line bandpass filter, six-port correlator, diode power detectors and two instrumentation amplifiers for recovering the baseband I/Q data. The EVM improvement process is assessed in terms of 64QAM modulation, and according to obtained results, EVM is reduced from 61% when using constant DC bias to 22% achieved with an LNA bias control algorithm for low input power (− 60 dBm) at the center frequency of 28 GHz. Moreover, the EVM is become less sensitive to input RF power, and also the dynamic range is improved more than 20 dB.

Simplified implementation of millimetre‐wave zero‐bias detector for an accurate detection in six‐port‐based receivers

In this Letter, a simplified design approach for zero-bias power detectors suited for integration in six-port receiver architectures is presented. The proposed concept uses the quadrature hybrid coupler as an effective way to improve the input impedance matching and linearity performance. The proposed solution has been experimentally validated through its implementation into a 60 GHz six-port receiver prototype to investigate its performance in detecting various M-ary quadrature amplitude modulation (M-QAM) signals. The obtained measurement results show a high accurate and linear detection responses for all investigated M-ary QAM modulation techniques (4-QAM, 16-QAM, 32-QAM). The variation in the error rates of the demodulated signals at the adjacent differential outputs is minimal (<1%), and the maximum error rate achieved does not exceed 5%. The obtained precision and linearity performances make the proposed structure highly suitable for the emerging millimetre-wave six-port receiver front-ends.

Improved analytical approach for studying the effect of diode power detector modelling on six-port communication receiver performance

Purpose The purpose of this paper is to study the effect of diode power detector modelling on six-port communication receiver performance. Design/methodology/approach Based on proposed and conventional squared diode model, six-port receiver’s demodulation and its error vector magnitude (EVM) performance due to hardware impairments are studied. Through considering both the models, the accuracy of proposed power detector model is compared to the squared model, and then both results are validated with envelope simulation (ENV) in advanced design system (ADS). Findings Comparing the numerical results with envelope simulation results proved that the proposed model is much more accurate than the conventional squared model for a wide range of input power levels. Originality/value Studying the receiver’s performance numerically, by considering the new proposed analytical approach for diode power detectors which is more accurate than the conventional squared model.

A seven-port receiver for MIMO wireless communications

A single front-end seven-port receiver is proposed and analyzed for multiple-input and multiple-output (MIMO) systems. This new architecture uses a single front-end in order to recieve two input RF modulated signals with Alamouti coding which reduces cost and complexity in the RF section compared to classical six-port based receivers adapted for $$2\times 2$$ MIMO application. We also analyzed the capability of our proposed single front-end seven-port receiver for 2 $$\times$$ N MIMO application with Alamouti coding, and evaluated its advantages and disadvantages versus classical MIMO six-port receivers. The performance of our proposed seven-port receiver is assesed in terms of two input QPSK modulated signals; then calculating the bit error rates (BERs). The obtained results demonstrate that the proposed seven-port receiver can be a candidate for using in MIMO communication systems.

Spatially Distributed Multi-Input Interferometric Receiver for 5G Wireless Systems and Beyond

This paper presents a spatially distributed multiinput direct conversion receiver architecture based on interferometric correlations of wave signals for fifth generation systems and beyond. The proposed receiver scheme inherits the advantages of conventional six-port receivers. The spatially distributed multi-input architecture is based on the use of a set of equally spaced four antenna elements instead of using a six-port junction composed of four hybrid couplers or other alternative circuit-based topologies. In this paper, the mathematical modeling of the proposed receiver is derived and presented. Then, an experimental test bench that is fabricated to operate around 5 GHz is introduced in order to validate the proposed scheme and its theoretical results. Various modulations including BPSK, QPSK, QAM-16, and QAM-32 have been successfully studied and demonstrated by this receiver at a relatively low date rate of 1 mega symbol per second with a maximum error vector magnitude of 10.3%. The maximum bit rate is fundamentally limited by the speed of power detectors, which is linked to their high rise time in our experiments. It is anticipated that multiple hundred megabits and gigabits per second can be achieved with the proposed direct conversion receiver if higher speed power detectors are used.

Concurrent Dual-Band Receiver Based on the Multi-Port Correlator for Wireless Applications

A concurrent dual-band receiver based on a single multiport correlator is proposed in this brief to down-convert dual-band radio frequency signals. The system configuration, output power, as well as its spectrum analysis are discussed, and then a generalized baseband signal recovery theory is put forward. Next, the calibration algorithm based on real-valued time-delay neural network, which can take the system impairments and signal distortions into consideration, is proposed to retrieve two baseband signals, simultaneously. Finally, the six-port receiver is tested under the common modulated signals, and the measured error vector magnitudes between the transmitted and the received signals are all less than 2%.

W-Band Graphene-Based Six-Port Receiver

We demonstrate a full-fledged millimeter-wave graphene-based six-port receiver frontend at 90 GHz employing graphene power detectors. Exploiting the high responsivity and wide dynamic range reported for the state-of-the-art graphene field-effect transistors (GFETs), graphene power detectors are demonstrated beyond the maximum oscillation frequency, $f_{\mathrm{ max}}$ , of the graphene transistor. The proposed circuit is fabricated on thinned SiC substrate and its functionality is verified by demodulation of 10-Mbps ON–OFF keying (OOK) digitally modulated signal.

Concurrent Dual-Band Low Intermediate Frequency Receiver Based on the Multiport Correlator and Single Local Oscillator

A concurrent dual-band low intermediate frequency receiver, which is based on the multiport correlator, is proposed in this letter. Only one single local oscillator signal is used to demodulate the dual-band RF signals at the same time, which greatly reduce the receiver complexity. The system configuration, output power theory, as well as the power spectrum are analyzed in detail, and then an appropriate baseband signal recovery theory is put forward. Finally, a concurrent dual-band six-port receiver is tested under the long-term evolution signals with 3- and 5-MHz bandwidths. The measured error vector magnitudes are all lower than 2%, which verify the proposed system structure and the signal recovery theory.

Millimeter-Wave Multifunction Multiport Interferometric Receiver for Future Wireless Systems

In this paper, a receiver architecture is presented which is capable of handling angle-of-arrival (AOA) detection as well as data communication. The architecture of the proposed multifunction receiver is based on the multiport interferometer technique, and it integrates two previously reported six-port-based system functions that were realized as two distinct six-port receivers (SPRs). This unification of two SPRs is mainly achieved through a new configuration of RF/local oscillator (LO) signals at input ports, a new phase processing of the input signals within a structured eight-port passive network and a complementary postprocessing of the signals at the output of detectors. Using two RF input ports and two LO input ports that are switched in two consecutive time slots, the proposed multiport-based receiver (MPR) can estimate the AOA with a simple signal-processing algorithm. The plurality of the RF input ports can cause self-interference for the received communication signals. Therefore, a phasing network within the proposed eight-port wave correlator is devised such that the incoming quadrature modulated RF carriers are demodulated in an orthogonal manner at four output ports. It is found that receiving communication signal from a nonzero AOA makes imbalance between demodulated components. To this end, the proposed MPR can first find the angular position of the other unit and then recover the demodulation components through data fusion and postprocessing. The mathematical model for the developed MPR is derived along with the development of an appropriate calibration technique, and its principal functionality is theoretically analyzed. In addition, a transceiver architecture based on this MPR is implemented, and prototyped for operation around 77 GHz. The techniques for hybrid millimeter-wave system integration are explained in this paper. The proposed concept is proven and concluded with satisfactory measurements for both functions. This unified multifunction MPR can find applications in the future vehicle-to-vehicle radios and joint radar-communication systems.

Concurrent Dual-Band Receiver Based on Novel Six-Port Correlator for Wireless Applications

A concurrent dual-band six-port receiver based on real-valued time-delay neural network (RVTDNN) is proposed in this paper to retrieve two baseband signals from a dual-band radio frequency signal, concurrently. Different from the traditional six-port correlator, the new passive circuit correlator, which is composed of one power divider and three quadrature couplers, has three inputs and three outputs, resulting in the decreased hardware complexity as well as circuit size, and a reduced power consumption for the system. The new six-port correlator, its output power as well as the baseband signal recovery theory are described and analyzed in detail. The calibration algorithm based on the RVTDNN is adopted to verify the feasibility of the concurrent dual-band receiver based on the proposed correlator circuit. Finally, a practical wideband six-port receiver test bench, which operates from 2 to 3 GHz, is built and tested using the common modulated signals. The calculated error vector magnitudes are all less than 2% verifying the correctness of this novel system implementation approach.

Novel Calibration Algorithm of Multiport Wideband Receivers Based on Real-Valued Time-Delay Neural Networks

In this paper, a novel calibration algorithm based on real-valued time-delay neural network (RVTDNN) is proposed for the multiport receiver to recover I/Q signals from the received modulated signals, especially from wideband signals. All the system impairments, including the nonideal six-port correlator, the nonlinearity of the diodes, and the memory effects under the excitation of the wideband signals, are taken into consideration. The RVTDNN, which has three layers, consists of four inputs and two outputs (in-phase and quadrature signals), and its parameters (biases and weights) are all real-valued and are determined by the backpropagation algorithm. Finally, the proposed calibration method is validated by a 2–18-GHz six-port receiver under 3G and 4G signals. The performance of the error vector magnitude between the transmitted signals and received signals is always less than 1.8%, which validates the correctness of the proposed model.

Finding the Initial Estimate for the Diode Bias Point in Multiport Receivers

In this brief, a novel methodology for estimating the initial diode bias voltage in multiport receivers was developed. We tested the methodology for four different Schottky diodes from different vendors (Win Corp, HP, Hitachi, and Siemens), but the process can be applied to any diode. The analysis shows that setting the initial value for the optimizer where the diode's output dc voltage to input power sensitivity is highest yields the fastest convergence time for the error vector magnitude (EVM) optimizer algorithm. This point is located at the inflection point of the first derivative of the $I{-}V$ curve fitting polynomial which was obtained in MATLAB and assures that the optimizer will not be trapped into local minima. To verify the results of this research, we used a Simulink model that emulates the radio frequency and digital base band parts of a six-port receiver. It was found that, by reducing the voltage difference between the estimated initial value and the optimum point, the optimizer needed less steps to reach the optimum value of the bias voltage. This work also provides the behavior of the variation of the initial estimates of the diode voltage with the polynomial degree. Hence, the necessary degree for the fitting polynomial can be determined based on the initial point variation analysis.

Optimization of EVM Through Diode Bias Control Using a Blind Algorithm Applied to Multiport Receivers

In this brief, we developed a detailed Simulink model that emulates the radio frequency and digital base band of a six-port receiver. In contrast to other results published in the literature, we not only provide a controlled continuous bias to the diodes. We propose a novel algorithm that reduces the error vector magnitude (EVM) by adaptively controlling the diode bias point. We will also show that when the algorithm is turned on in the model, the EVM becomes less sensitive to variations in the diode bias conditions. Another key feature of optimum diode bias control is that the local oscillator (LO) power requirements decrease and that the EVM is not sensitive to LO power variation. Results presented here show that for an LO power variation of more than 10 dB, we notice no EVM variation.

Performance Analysis of a Six-Port Receiver in a WCDMA Communication System including a Multipath Fading Channel

Third generation communication systems require receivers with wide bandwidth of operation to support high transmission rates and are also reconfigurable to support various communication standards with different frequency bands. An ideal software defined radio (SDR) will be the absolute answer to this requirement but it is not achievable with the current level of technology. This paper proposes the use of a six-port receiver (SPR) front-end (FE) in a WCDMA communication system. A WCDMA end-to-end physical layer MATLAB demo which includes a multipath channel distortion block is used to determine the viability of the six-port based receiver. The WCDMA signal after passing through a multipath channel is received using a constructed SPR FE. The baseband signal is then calibrated and corrected in MATLAB. The six-port receiver performance is measured in terms of bit error rate (BER). The signal-to-noise ratio (SNR) of the transmittedIQdata is varied and the BER profile of the communication system is plotted. The effect of the multipath fading on the receiver performance and the accuracy of the calibration algorithm are obtained by comparing two different measured BER curves for different calibration techniques to the simulated BER curve of an ideal receiver.

Performance Driven Six-Port Receiver and Its Advantages over Low-IF Receiver Architecture

This paper provides an extensive analysis of the performance of a six-port based direct conversion receiver (SPR) in terms of signal quality, dynamic range, noise figure, ports matching, isolation, bandwidth, and cost. Calibration technique using multimemory polynomials has been adopted in order to improve the signal quality of the six-port receiver. The performances of the calibrated receiver are then compared with the performances of a commercially availableI-Qdemodulator used as a low-IF receiver. The main advantages and disadvantages of the SPR compared to the low-IF receiver are highlighted. The major advantages of the SPR come in terms of its available input frequency bandwidth and the low power requirement. The SPR system requires no external bias supply but suffers in terms of the available conversion gain. A better port matching of the SPR can be guaranteed over a wide frequency bandwidth, which mixer based receiver systems lack. The main component limiting the performance of a SPR is the diode detector. A faster and a better diode detector will alleviate some of the problems highlighted in this paper. The SPR system is calibratable and its error-vector-magnitude performance can be made better than theI-Qdemodulator used as a low-IF receiver.

Concurrent Dual-Band Six-Port Receiver for Multi-Standard and Software Defined Radio Applications

This paper proposes a novel concurrent dual-band receiver architecture that uses only one six-port correlator circuit to downconvert two signals in two different bands concurrently. The receiver is reconfigurable over a broadband to simultaneously receive two different signals with different modulation techniques and bandwidths. There are no limitations on the carrier frequencies of the two signals except that they have to be within the bandwidth of the six port receiver. The mathematical model for the receiver is derived and subsequently implemented to evaluate its performance. This approach shows that, by analytically choosing the frequencies of the two local oscillator signals sent into the six-port correlator, the in-phase (I) and the quadrature (Q) components of each of the two input RF signals can be obtained from the filtered high-pass and low-pass components of the diode detectors outputs. A black box model, which uses a modified memory polynomial, is used to calibrate the receiver. The calibration constants are estimated by sending a training signal of similar characteristics as the signal to be received. Two signals pairs with different modulation types are received to verify the model, and to evaluate the performance and test the robustness of the receiver. A 64-QAM signal at 2.5 GHz and a 16-QAM signal at 3.0 GHz, both with a data rate of 2 Mbps are received. The measured EVMs were 1.9% for the 64-QAM and 1.8% for the 16-QAM. Real communication signals, WCDMA and LTE were also received concurrently with measured EVMs of 1.9% and 2.0%, respectively. A bit error rate (BER) profile of the receiver for a 16QAM and 64QAM, both at 2Mbps is also plotted to evaluate the receiver.